Systems for the large scale painting of motor vehicles, vehicle components, fixtures, appliances, and other mass produced items of manufacture are relatively complex and include fluid lines, tanks, valves, and the like. Likewise other fluid handling systems such as food or chemical processing equipment include similar structures. The internal surfaces of such systems are often cleaned by pumping one or more cleaning fluids therethrough and in some instances, such cleaning fluids include a particulate material therein which aids in the cleaning process. In a typical cleaning process, a number of precleaners and/or rinse fluids are also passed through the system prior to and/or after the use of the particulate containing cleaning fluid.
In the context of cleaning a paint delivery system, various cleaning fluids of the type which are the subject of this present patent application function to solvate deposits and remove debris from a paint line system. These deposits and debris can include hardened paint residues as well as particulates resultant from contaminants in the paint, metal particles which are shed by valving, pipe joints, pumps and the like, traces of pigment and so forth. It is generally desirable that line cleaning compositions have a relatively low viscosity so that the agents can effectively flow through and penetrate all portions of the delivery system. In addition, it is generally desirable to avoid high viscosity fluids, since pumping, valving and other components of the system are not engineered for handling such high viscosity fluids.
While low viscosity cleaning compositions are desired, there are problems associated therewith, since low viscosity fluids are not very effective at suspending particulate materials. This is not a problem when the fluid is flowing relatively rapidly; but when the fluid flow slows as a result of passing through sumps or other drops in the system, or when flow is terminated, suspended particles can rapidly settle out of low viscosity fluids thereby negating the effects of the cleaning process. But, as noted above, use of high viscosity cleaning fluids is undesirable, and in some instances can actually damage pumps, valves and other components. Therefore, it will be appreciated that there is a need for a class of line cleaning compositions including precleaners, cleaners, purgents, rinses, scouring agents and the like which are capable of efficiently suspending particulate matter therein. Such fluids should also be compatible with the structure and operational requirements of paint delivery systems and associated cleaning equipment.
In many instances, the industry is now turning to the use of water-based paints and other process fluids. Hence, there is a need for paint line cleaning compositions which are compatible with water-based paints. Such compositions should be effective in removing residues of water-based paints and in purging lines of water-based paints. Such compositions must also be compatible with subsequently introduced water-based process fluids.
As will be explained hereinbelow, the present invention provides a system of line cleaning compositions which have very specifically controlled rheological properties. The compositions of the present invention have a very high resting viscosity, but thin to a low viscosity when a particular shear threshold is passed. In this manner, the fluids of the present invention are very efficient at suspending and retaining particulate matter; but, their viscosity thins in use to enable effective cleaning and prevent any mechanical burden or damage to associated equipment. These and other advantages of the invention will be discussed in detail hereinbelow.